Ceramic Armor

Abstract

A dense, hard body having good fracture toughness, hardness and a high capacity to absorb impacts which is also useful as lightweight armor. The body is an eutectic of either (a) two carbides selected from boron carbide (B 4 C), silicon carbide (SiC), titanium carbide (TiC), tantalum carbide (TaC), tungsten carbide (WC), zirconium carbide (ZrC) and hafnium carbide (HfC); or (b) one of the above carbides and at least one boride of an element of group IVa, Va or VIa of the Periodic Table. The molten eutectic, e.g. a ternary composition of B 4 C, SiC and TiB 2 , may be generally directionally cooled so its lamellar microstructure is oriented relative to a large surface of the body.

1 . A method of making an armor body having a thickness sufficient to stop a bullet and a surface of greater dimension transverse to such thickness, which method comprises: 
 heating a mixture of particulate materials which will form an eutectic to a temperature sufficient to form a molten eutectic,    said mixture including at least: 
 (a) two carbides selected from boron carbide, silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, zirconium carbide and hafnium carbide; or  
 (b) one of the above said carbides plus at least one boride of an element of group IVa, Va or VIa of the Periodic Table, and  
   cooling said molten eutectic under controlled conditions such that a body having a surface of such dimension is formed, which body has a directionally oriented lamellar microstructure,    whereby the resulting body has a high capacity to absorb impacts and has high fracture toughness.    
     
     
         2 . The method of  claim 1  wherein said mixture is heated to a temperature at least about 50° C. above the eutectic melting point thereof to create a substantially totally molten eutectic.  
     
     
         3 . The method of  claim 1  wherein said mixture is maintained molten for at least about 5 minutes and is cooled so that said lamellar microstructure is generally parallel to said surface.  
     
     
         4 . The method of  claim 3  wherein said molten mixture is initially cooled at a rate of between about 5° and about 15° C./minute until a temperature of about 1900° C. is reached.  
     
     
         5 . The method of  claim 4  wherein said heating and cooling are carried out in an inert atmosphere.  
     
     
         6 . The method according to  claim 1  wherein said mixture is heated in a crucible to a temperature above 2000° C., which crucible is coated with a barrier coating that prevents interaction between the molten eutectic and the material from which the crucible is made that might contaminate the resultant eutectic.  
     
     
         7 . The method of  claim 1  wherein said mixture includes particulate carbides or carbides and borides in amounts within at least about 5 weight % of a stiochiometric eutectic composition thereof.  
     
     
         8 . The method of  claim 1  wherein said mixture includes (a) particulate SiC and either TiB 2  or ZrB 2 , (b) particulate SiC and B 4 C; or (c) particulate B 4 C and either ZrB 2  or TiB 2 .  
     
     
         9 . The method of  claim 1  wherein said mixture includes two of said carbides and one said boride in particulate form.  
     
     
         10 . The method of  claim 9  wherein said mixture includes SiC, B 4 C and TiB 2 .  
     
     
         11 . The method of  claim 1  wherein said mixture includes particles of not greater than about 2 μm in size.  
     
     
         12 . The method of  claim 11  wherein said mixture is made by ball milling said particulate materials so that an intimate interdispersion of said particles is heated above the eutectic melting point.  
     
     
         13 . An armor body which comprises a structure having a thickness sufficient to stop a bullet impacting against a surface of greater dimensions than such thickness and oriented generally perpendicular thereto, said structure consisting essentially of an eutectic composition which comprises either 
 (a) two carbides selected from boron carbide, silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, zirconium carbide and hafnium carbide; or    (b) one of the above said carbides and at least one boride of an element of group IVa, Va or VIa of the Periodic Table,    said structure having a lamellar microstructure that is generally directionally oriented relative to said surface thereof, whereby said armor body has a high capacity to absorb impacts against said surface and a high fracture toughness.    
     
     
         14 . The armor body of  claim 13  wherein said eutectic comprises silicon carbide and either titanium boride or zirconium boride.  
     
     
         15 . The armor body of  claim 13  wherein said eutectic comprises silicon carbide and boron carbide.  
     
     
         16 . The armor body of  claim 13  wherein said eutectic comprises boron carbide and either titanium boride or zirconium boride.  
     
     
         17 . The armor body of  claim 13  wherein said eutectic comprises boron carbide, silicon carbide and titanium boride.  
     
     
         18 . A dense, hard body having good fracture toughness, which body consists essentially of an eutectic composition that comprises either 
 (a) two carbides selected from boron carbide (B 4 C), silicon carbide (SiC), titanium carbide (TiC), tantalum carbide (TaC), tungsten carbide (WC), zirconium carbide (ZrC) and hafnium carbide (HfC); or    (b) one of the above said carbides and at least one boride of an element of group IVa, Va or VIa of the Periodic Table,    said body having a lamellar microstructure that is generally directionally oriented relative to a main surface of said body, and said body having a high capacity to absorb impacts from a direction transverse to said main surface and a high fracture toughness.    
     
     
         19 . The body of  claim 18  which said body has a hardness of about 2400 kg/mm 2  on the Knoop scale and a fracture toughness at least about 4 MPa√{square root over (m)}.  
     
     
         20 . The body of  claim 18  wherein said eutectic comprises B 4 C, SiC and TiB 2 .